Re: [PATCH net-next 14/15] mlx4: support BIG TCP packets
From: Eric Dumazet <edumazet@google.com>
Date: 2022-02-03 15:54:59
() On Thu, Feb 3, 2022 at 5:04 AM Tariq Toukan [off-list ref] wrote:
On 2/3/2022 3:51 AM, Eric Dumazet wrote:quoted
From: Eric Dumazet <edumazet@google.com> mlx4 supports LSOv2 just fine. IPv6 stack inserts a temporary Hop-by-Hop header with JUMBO TLV for big packets. We need to ignore the HBH header when populating TX descriptor. Tested: Before: (not enabling bigger TSO/GRO packets) ip link set dev eth0 gso_ipv6_max_size 65536 gro_ipv6_max_size 65536 netperf -H lpaa18 -t TCP_RR -T2,2 -l 10 -Cc -- -r 70000,70000 MIGRATED TCP REQUEST/RESPONSE TEST from ::0 (::) port 0 AF_INET6 to lpaa18.prod.google.com () port 0 AF_INET6 : first burst 0 : cpu bind Local /Remote Socket Size Request Resp. Elapsed Trans. CPU CPU S.dem S.dem Send Recv Size Size Time Rate local remote local remote bytes bytes bytes bytes secs. per sec % S % S us/Tr us/Tr 262144 540000 70000 70000 10.00 6591.45 0.86 1.34 62.490 97.446 262144 540000 After: (enabling bigger TSO/GRO packets) ip link set dev eth0 gso_ipv6_max_size 185000 gro_ipv6_max_size 185000 netperf -H lpaa18 -t TCP_RR -T2,2 -l 10 -Cc -- -r 70000,70000 MIGRATED TCP REQUEST/RESPONSE TEST from ::0 (::) port 0 AF_INET6 to lpaa18.prod.google.com () port 0 AF_INET6 : first burst 0 : cpu bind Local /Remote Socket Size Request Resp. Elapsed Trans. CPU CPU S.dem S.dem Send Recv Size Size Time Rate local remote local remote bytes bytes bytes bytes secs. per sec % S % S us/Tr us/Tr 262144 540000 70000 70000 10.00 8383.95 0.95 1.01 54.432 57.584 262144 540000 Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Tariq Toukan <tariqt@nvidia.com> --- .../net/ethernet/mellanox/mlx4/en_netdev.c | 3 ++ drivers/net/ethernet/mellanox/mlx4/en_tx.c | 47 +++++++++++++++---- 2 files changed, 41 insertions(+), 9 deletions(-)diff --git a/drivers/net/ethernet/mellanox/mlx4/en_netdev.c b/drivers/net/ethernet/mellanox/mlx4/en_netdev.c index c61dc7ae0c056a4dbcf24297549f6b1b5cc25d92..76cb93f5e5240c54f6f4c57e39739376206b4f34 100644 --- a/drivers/net/ethernet/mellanox/mlx4/en_netdev.c +++ b/drivers/net/ethernet/mellanox/mlx4/en_netdev.c@@ -3417,6 +3417,9 @@ int mlx4_en_init_netdev(struct mlx4_en_dev *mdev, int port, dev->min_mtu = ETH_MIN_MTU; dev->max_mtu = priv->max_mtu; + /* supports LSOv2 packets, 512KB limit has been tested. */ + netif_set_tso_ipv6_max_size(dev, 512 * 1024); + mdev->pndev[port] = dev; mdev->upper[port] = NULL;diff --git a/drivers/net/ethernet/mellanox/mlx4/en_tx.c b/drivers/net/ethernet/mellanox/mlx4/en_tx.c index 817f4154b86d599cd593876ec83529051d95fe2f..c89b3e8094e7d8cfb11aaa6cc4ad63bf3ad5934e 100644 --- a/drivers/net/ethernet/mellanox/mlx4/en_tx.c +++ b/drivers/net/ethernet/mellanox/mlx4/en_tx.c@@ -44,6 +44,7 @@ #include <linux/ipv6.h> #include <linux/moduleparam.h> #include <linux/indirect_call_wrapper.h> +#include <net/ipv6.h> #include "mlx4_en.h"@@ -635,19 +636,28 @@ static int get_real_size(const struct sk_buff *skb, struct net_device *dev, int *lso_header_size, bool *inline_ok, - void **pfrag) + void **pfrag, + int *hopbyhop) { struct mlx4_en_priv *priv = netdev_priv(dev); int real_size; if (shinfo->gso_size) { *inline_ok = false; - if (skb->encapsulation) + *hopbyhop = 0; + if (skb->encapsulation) { *lso_header_size = (skb_inner_transport_header(skb) - skb->data) + inner_tcp_hdrlen(skb); - else + } else { + /* Detects large IPV6 TCP packets and prepares for removal of + * HBH header that has been pushed by ip6_xmit(), + * mainly so that tcpdump can dissect them. + */ + if (ipv6_has_hopopt_jumbo(skb)) + *hopbyhop = sizeof(struct hop_jumbo_hdr); *lso_header_size = skb_transport_offset(skb) + tcp_hdrlen(skb); + } real_size = CTRL_SIZE + shinfo->nr_frags * DS_SIZE + - ALIGN(*lso_header_size + 4, DS_SIZE); + ALIGN(*lso_header_size - *hopbyhop + 4, DS_SIZE); if (unlikely(*lso_header_size != skb_headlen(skb))) { /* We add a segment for the skb linear buffer only if * it contains data */@@ -874,6 +884,7 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev) int desc_size; int real_size; u32 index, bf_index; + struct ipv6hdr *h6; __be32 op_own; int lso_header_size; void *fragptr = NULL;@@ -882,6 +893,7 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev) bool stop_queue; bool inline_ok; u8 data_offset; + int hopbyhop; bool bf_ok; tx_ind = skb_get_queue_mapping(skb);@@ -891,7 +903,7 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev) goto tx_drop; real_size = get_real_size(skb, shinfo, dev, &lso_header_size, - &inline_ok, &fragptr); + &inline_ok, &fragptr, &hopbyhop); if (unlikely(!real_size)) goto tx_drop_count;@@ -944,7 +956,7 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev) data = &tx_desc->data; data_offset = offsetof(struct mlx4_en_tx_desc, data); } else { - int lso_align = ALIGN(lso_header_size + 4, DS_SIZE); + int lso_align = ALIGN(lso_header_size - hopbyhop + 4, DS_SIZE); data = (void *)&tx_desc->lso + lso_align; data_offset = offsetof(struct mlx4_en_tx_desc, lso) + lso_align;@@ -1009,14 +1021,31 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev) ((ring->prod & ring->size) ? cpu_to_be32(MLX4_EN_BIT_DESC_OWN) : 0); + lso_header_size -= hopbyhop; /* Fill in the LSO prefix */ tx_desc->lso.mss_hdr_size = cpu_to_be32( shinfo->gso_size << 16 | lso_header_size); - /* Copy headers; - * note that we already verified that it is linear */ - memcpy(tx_desc->lso.header, skb->data, lso_header_size); + if (unlikely(hopbyhop)) { + /* remove the HBH header. + * Layout: [Ethernet header][IPv6 header][HBH][TCP header] + */ + memcpy(tx_desc->lso.header, skb->data, ETH_HLEN + sizeof(*h6)); + h6 = (struct ipv6hdr *)((char *)tx_desc->lso.header + ETH_HLEN); + h6->nexthdr = IPPROTO_TCP; + /* Copy the TCP header after the IPv6 one */ + memcpy(h6 + 1, + skb->data + ETH_HLEN + sizeof(*h6) + + sizeof(struct hop_jumbo_hdr), + tcp_hdrlen(skb)); + /* Leave ipv6 payload_len set to 0, as LSO v2 specs request. */Hi Eric, Many thanks for your patches. Impressive improvement indeed! I am concerned about not using lso_header_size in this flow. The num of bytes copied here might be out-of-sync with the value provided in the descriptor (tx_desc->lso.mss_hdr_size). Are the two values guaranteed to be equal?
I think they are equal. get_real_size() sets : *lso_header_size = skb_transport_offset(skb) + tcp_hdrlen(skb); Also, BIG TCP is supporting native IPv6 + TCP only at this moment.
I think this is an assumption that can get broken in the future by unaware patches to the kernel stack.
Changes are self-contained in drivers/net/ethernet/mellanox/mlx4/en_tx.c, functions get_real_size() and mlx4_en_xmit()
Thanks, Tariqquoted
+ } else { + /* Copy headers; + * note that we already verified that it is linear + */ + memcpy(tx_desc->lso.header, skb->data, lso_header_size); + } ring->tso_packets++; i = shinfo->gso_segs;